Not all Juggs are Sett. He's is designed to be a Tank-buster. Q has bonus damage based on enemy Max Health, W is true damage, and R's damage scales with enemy bonus health. Legit 3/4 skills hit tanks harder than carries.
Taken from the Fandom page on Juggs:
"Juggernauts are melee titans who relentlessly march down the opposition and devastate those foolish enough to get within their grasp. They are the only subclass who excel at both dealing and taking significant amounts of damage, but in turn they have a tough time closing in on targets due to their low range and extremely limited mobility."
People pick tanks to have an impact late, when team fights are a much bigger deal. They utilize their CC to either peel for ADC's or lock down the opponent. They take time to get tanky, but can be invaluable.
Sett (for better or worse) also has gap-closer in his Q, a monster shield on the W, and a mutli-man stun on his E, making him relevant regardless of the game state. Other Juggs either have their damage fall off
or need time to get their damage scaling up
. Sett starts our tough, and really never drops off.
As for the question at the end of the OP: Riot actively hates silences, mana-burns, etc. There has never been a mana-burn skill in the game to my knowledge, and only a select few have silences left:
.
and
all had their silences removed years ago.